1Field of the Invention
The present invention relates to a magnetic lock closure device making use of the attractive action provided by a permanent magnet.
2. Description of the Prior Art
Conventionally, there is known a magnetic lock closure device that can be used on bags such as women's handbags, baggage, and the like as a locking device, or on clothing accessories such as waist belts. In either case, the magnetic lock closure device comprises a first part including an annular permanent magnet and a first ferromagnetic plate attached to one side of the permanent magnet that provides one polarity, and a second part including a second ferromagnetic plate which may be removably attached to the other side of the permanent magnet that provides the opposite polarity. The first part is completely enclosed by a nonmagnetic cover, and the first ferromagnetic plate may or may not have a rod at the center extending therefrom, which is also ferromagnetic. On the second part, the second ferromagnetic plate has a rod at the center extending therefrom, which is also ferromagnetic. When those two parts are to be coupled together, the second ferromagnetic plate can be engaged with the first part by engaging the rod on the second part with the rod on the first part or directly with the first ferromagnetic plate which in this case has no such rod, through the bore of the permanent magnet and cover. The two parts can be decoupled by pulling the second part away from the first part.
When the conventional magnetic lock closure device is employed for a handbag, for example, the first part which contains the permanent magnet is mounted on the body side of the handbag, and the second part is mounted on the flap side of the handbag. When the first and second parts are to coupled together under the attacting force of the first part, the second ferromagnetic plate is placed on the first part so that the rod on the second ferromagnetic plate can first engage the portion of the cover that is located between the outer marginal periphery of the annular permanent magnet and the periphral marginal edge of the bore through the magnet. This is because that portion of the outer cover or permanent magnet provides the highest magnetic flux density which tends to attract the rod on the second ferromagnetic plate more coercively than the other areas when the second part is placed on the first part. Then, an attempt is made to locate the bore through the outer cover and permanent magnet and force the rod on the second ferromagnetic plate into the bore by the most coercive attracting action of that portion. As the rod on the second ferromagnetic plate is magnetically attracted by that portion, it can only be moved away from that highest density area toward the bore in a zigzag fashion rather than directly, before it can successfully engage the bore. This may disadvantagously cause damage such as scratches on the outer cover.
Usually and in practice, prospective customers check to see if the devices on handbags or other articles will work well by trying to couple or decouple the two parts before they have decided upon one of their choice. In particular, the coupling action which involves the sliding motion may cause damage as described above that may degrade the commercial value of the articles. One practically proposed method whereby such damage can be prevented is to provide an additional protective sealing over the outer cover, or to provide a mesh pattern on the outer cover that hides any possible damages.
Another suggested method is to minimize the sliding motion of the rod on the second ferromagnetic plate onto the outer cover. This method may consist of providing a concavely-formed surface on the side of the permanent magnet that meets with the second ferromagnetic plate. The outer cover also has the corresponding surface on that side. This particular form may serve to guide the rod on the second ferromagnetic plate toward the center bore with minimum effort and therefore with minimum sliding motion. This particular form may be obtained by grinding or polishing an annular permanent magnet to conform to such form, but the grinding or polishing process is not adequate for the permanent magnet in particular, since the high dimensional or precision requirements that the permanent magnet must meet cannot be provided by the grinding or polishing process. This will disadvantageously affect the assembly process of the device that contains the thus formed permanent magnet as well as the other subassembly parts. Thus, the device that incorporates such a formed permanent magnet may not provide an attracting action that is strong enough to couple its two parts together magnetically. It is therefore to be noted that the products which have been manufactured in that manner may include many defective ones, which means a lower productivity or yield.
As an alternative solution to the above disadvantage, it has been suggested that an annular permanent magnet be provided with an additional part that may be formed from a ferromagnetic material as a yoke having a concavely formed surface on its one side. This yoke may eliminate the need of forming the permanent magnet itself, but will also increase the number of the component parts to be assembled. As the number of the component parts is increased, the accummulated dimensional errors for each individual part will become greater. Thus, the precision problem that will occur during the assembly process remains unsolved.